Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for facilitating the connection of tubulars of a drilling rig.
Description of the Related Art
In the construction and completion of oil or gas wells, a drilling rig is constructed on the earth's surface to facilitate the insertion and removal of tubular strings into a wellbore. The drilling rig includes a platform and power tools such as an elevator and a spider to engage, assemble, and lower the tubulars into the wellbore. The elevator is suspended above the platform by a draw works that can raise or lower the elevator in relation to the floor of the rig. The spider is mounted in the platform floor. The elevator and spider both have slips that are capable of engaging and releasing a tubular, and are designed to work in tandem. Generally, the spider holds a tubular or tubular string that extends into the wellbore from the platform. Traditionally, the elevator engages a new tubular and aligns it over the tubular string being held by the spider. A power tong and a spinner are then used to thread the upper and lower tubulars together. Once the tubulars are joined, the spider disengages the tubular string and the elevator lowers the tubular string through the spider until the elevator and spider are at a predetermined distance from each other. The spider then re-engages the tubular string and the elevator disengages the string and repeats the process. This sequence applies to assembling tubulars for the purpose of drilling a wellbore, running casing to line the wellbore, or running wellbore components into the well. The sequence can be reversed to disassemble the tubular string.
During the drilling of a wellbore, a drill string is made up and is then necessarily rotated in order to drill. Historically, a drilling platform includes a rotary table and a gear to turn the table. In operation, the drill string is lowered by an elevator into the rotary table and held in place by a spider. A Kelly is then threaded to the string and the rotary table is rotated, causing the Kelly and the drill string to rotate. After thirty feet or so of drilling, the Kelly and a section of the string are lifted out of the wellbore and additional drill string is added.
The process of drilling with a Kelly is expensive due to the amount of time required to remove the Kelly, add drill string, reengage the Kelly, and rotate the drill string. In order to address these problems, top drives were developed.
For example, FIG. 1 shows a drilling rig 100 configured to connect and run casings into a newly formed wellbore 180 to line the walls thereof. As shown, the rig 100 includes a top drive 200, an elevator 120, and a spider 400. The rig 100 is built at the surface 170 of the well. The rig 100 includes a traveling block 110 that is suspended by wires 150 from draw works 105 and holds the top drive 200. The top drive 200 has a gripping tool 301 for engaging the inner wall of the casing 130 and a motor 240 to rotate the casing 130. The motor 240 may rotate and thread the casing 130 into the casing string 130 held by the spider 400. The gripping tool 301 facilitates the engagement and disengagement of the casing 130 without having to thread and unthread the casing 130 to the top drive 200. Additionally, the top drive 200 is coupled to a railing system 140. The railing system 140 prevents the top drive 200 from rotational movement during rotation of the casing string 130, but allows for vertical movement of the top drive 200 under the traveling block 110.
In FIG. 1, the gripping tool 301 is shown engaged to casing 130. The casing 130 is placed in position below the top drive 200 by the elevator 120 in order for the gripping tool 301 to engage the casing 130. Additionally, the spider 400, disposed on the platform 160, is shown engaged around a casing string 130 that extends into wellbore 180. Once the casing 130 is positioned above the casing string 130, the top drive 200 can lower and thread the casing 130 into the casing string 130 in the wellbore, thereby extending the length of the casing string 130. Thereafter, the extended casing string 130 may be lowered into the wellbore 180.
FIG. 1 illustrates a drilling rig 100 that lifts and installs individual casing sections 130′. FIG. 2 illustrates a drilling rig 100′ that lift three casing sections 130′ that have been pre-coupled. FIG. 2 illustrates a first set of three joined casing sections 130′ attached to the top drive 200 and positioned above the casing string 130 in the spider 400. FIG. 2 also illustrates two additional sets of three joined casing sections 130′ positioned for lifting by the elevator 120 (described below).
FIG. 3 illustrates the gripping tool 301 engaged to the casing string 130 after the casing string 130 has been lowered through a spider 400. The spider 400 is shown disposed on the platform 160. The spider 400 comprises a slip assembly 440 including a set of slips 410 and piston 420. The slips 410 are wedge-shaped and constructed and arranged to slidably move along a sloped inner wall of the slip assembly 440. The slips 410 are raised or lowered by the piston 420. When the slips 410 are in the lowered position, they close around the outer surface of the casing string 130. The weight of the casing string 130 and the resulting friction between the casing string 130 and the slips 410 force the slips downward and radially inward, thereby tightening the grip of the slips 410 on the casing string 130. When the slips 410 are in the raised position as shown, the slips 410 are opened and the casing string 130 is free to move axially relative to the slips 410.
The above-described method of connecting tubulars is complicated and time-consuming, requiring the elevator 120 and gripping tool 301 to alternately grip and release the tubulars in a particular sequence. Thus, there is a need for an apparatus and method that simplifies the connection of tubulars.